Ni(II)-Based one dimensional coordination polymers for environmental remediation: design, topology, magnetism and the selective adsorption of cationic dyes

Herein, two Ni(ii)-based one-dimensional (1D) coordination polymers (CPs), namely, [Ni(Hpdc)(H2O)(mu-H2O)](n) (CP-1) and [Ni(pyc)(2)(H2O)](n) (CP-2), where H(3)pdc = 3,5-pyrazoledicarboxylic acid and Hpyc = pyrazine-2-carboxylic acid, were successfully synthesized under solvothermal reaction conditions. Both the polymers were thoroughly characterized through single-crystal X-ray diffraction, UV-visible, FTIR and TGA techniques. Variable-temperature magnetic-susceptibility data indicated the presence of antiferromagnetic (AF) interactions in both the CPs. The crystal structures showed hexa-coordinated environments around the Ni(ii) ions. The 2,2,4C1 and 2C1 topologies of the resulting 4-c net and 2-c net uninodals were acquired for CP-1 and CP-2, respectively. The CPs were then exploited for their adsorption properties towards organic pollutants such as organic dyes. Both the CPs were demonstrated to have the structural features necessary to adsorb the cationic dyes from waste water. The CPs adsorbed the cationic dyes (MB and Rh-B) even in the presence of an anionic dye, giving rise to the separation of the two types of dyes. Moreover, with evidence from the kinetics of the reaction, it could be concluded that both CPs bestowed the reaction with pseudo-second-order kinetics. The plausible mechanism associated with the adsorption of cationic dyes was also elaborated, which suggested that mainly electrostatic, H-bonding and pi-pi interactions were responsible for the adsorption process. Thus, the design and characterization of polymer-based adsorbents for the treatment of wastewater has potential as an emerging field and deserves to be addressed in future endeavours.